Preform or matrix tubular structure for casing a well

ABSTRACT

The tubular structure comprises at least a braid of flexible strands (10) comprising fibers (100) that cross over with a certain amount of play so that the structure is capable of expanding radially while shrinking axially when pressure is applied to the inside of the preform or the matrix.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a preform or matrix tubular structurefor casing a well, in particular a drilled oil well.

In the present description, and in the claims, the term "casing" is usedto designate a tube for consolidating a well, the term "preform" is usedto designate a tubular structure which is initially flexible and whichis subsequently hardened to bond intimately and permanently against thewall of a well (thus constituting a casing), and the term "matrix" isused to designate a structure that is flexible and recoverable, servingas a tool for expanding a preform and pressing it against the wall ofthe well prior to setting.

The term "production tubing" is used to designate a smaller diametercoaxial tube inside a casing and serving to convey the fluid produced bythe well (in particular water or oil).

The tubing is centered and sealed relative to the casing by means of ahydraulically inflatable plug, commonly known as a "packer".

2. Art Background

For casing an oil well, and for similar applications, flexible andsettable tubular preforms have already been proposed that are designedto be instaled while in the folded state--a state in which they occupylittle radial size--and then to be radially unfolded by applyinginternal pressure thereto. In that technique, which is described inparticular in documents FR-A-2 662 207 and FR-A-2 668 241, the preform,after being radially deployed, possesses a shape that is accuratelycylindrical, and of well-determined diameter.

After being installed in a well or in pipework, the wall of the preformis caused to set, e.g. by polymerizing a wall which is composite instructure being made up of a resin impregnating filamentary sleeves. Thesleeves ensure the the preform is radially inextensible.

In those techniques, it is necessary to provide for the diameter of thedeployed casing to be slightly smaller than the diameter of the hole tobe cased so that the wall of the hole does not alter the cylindricalshape of the casing. In general, even if it is very small or evenvanishes in places, the annular space that is formed in this way must befilled with cement to complete sealing between the hole and theinstalled casing.

In addition, while in its folded state, the tubular preform has a radialsection that is less than about half its developed radial section, andin most cases that suffices, but in some applications it can beinsufficient. That is why, the object of the present invention is tosolve the above problem by proposing a preform whose structure is ofdeformable shape suitable for bearing against the walls of the hole tobe cased (or of the casing to be lined) while nevertheless not exceedingcertain limits, with deformation being controlled and variable as afunction of various applications.

Another object of the invention is to provide a preform whose degree ofexpansion is considerably greater than that obtained with known devicesof the above-specified kind, expansion of the preform taking place intwo steps, initially by radial deployment, and subsequently by radialexpansion.

SUMMARY OF THE INVENTION

To achieve this result, the invention provides a braided tubularstructure which is described below, the structure being equallyapplicable to a radially-expandable matrix, i.e. to a removable (andreusable) tool serving to expand a preform for the purpose of casing awell, and regardless of whether the preform possesses the structure ofthe invention.

According to the invention, these results are achieved by the fact thatthe proposed preform or matrix tubular structure comprises at least onebraid of flexible strands made up of fibers that cross over with acertain amount of play so as to enable the structure to expand radiallywhile shrinking axially under the effect of excess pressure beingapplied inside the preform or the matrix.

In a preferred embodiment, the braiding comprises two series of strandscrossing over symmetrically on either side of the generator lines of thetubular structure, i.e. relative to its longitudinal axis, with thestrands in each series being mutually parallel.

When the structure is in its radially-contracted state, each of theseries of strands preferably lies relative to the longitudinal axis atan acute angle lying in the range 10° to 30°, and preferably about 20°,whereas the same angle lies in the range 50° to 70° when the structureis in its radially-expanded state.

The strands are preferably flat, taking up the shape of tapes.

The tubular preform that also forms subject matter of the invention isremarkable by the fact that it possesses a structure as defined above.

In a preferred embodiment, the preform possesses a wall of compositematerial, made of a medium that is fluid and settable in which saidstructure is embedded, the medium being confined between inner and outerskins of elastic material.

The inner skin could be the wall of the matrix itself.

Said material is preferably a settable resin, e.g. a resin thatpolymerizes when hot.

In a possible embodiment, the outer skin has patterns in relief, e.g. inthe form of annular swellings.

Advantageously, the structure comprises a plurality of elementarycoaxial tubular structures of the invention, with the various tubularstructures being nested one within another with the possibility ofmutual sliding.

The structure is preferably sufficiently flexible to be capable of beingfolded up longitudinally when the structure is in itsradially-contracted state.

Thus, if the structure constitutes a preform, while it is being put intoplace in the well or the pipework, the procedure begins by unfolding itfrom one end so as to give it a shape that is approximately cylindrical,after which it is subjected to radial expansion by deforming thestructure; deployment by unfolding and subsequent expansion is performedby applying a fluid to the inside of the preform.

The invention also provides a tubular matrix having a wall that isflexible and radially expandable, that is designed to press radiallyagainst the inside wall of a preform before and during setting thereoffor the purpose of casing a well, and in particular an oil well.

The wall of the matrix is provided with at least one tubular structurebonded to an elastic support (likewise tubular, and leakproof) andcomprising a braid of flexible strands made up of fibers which crossover with a certain amount of play, such that the structure and itssupport are capable of expanding together in a radial direction whileshrinking in the axial direction under the effect of internal pressure,whereas, conversely, they are capable of shrinking radially andextending axially under the effect of internal suction (vacuum) and/orof axial traction.

In an advantageous embodiment of a matrix of the invention, the tubularstructure is inserted between two elastic membranes, an inner membraneand an outer membrane, the assembly forming an inflatable sleeve that isfitted with a tube for feeding fluid into the sleeve.

In an embodiment, such a matrix is fixed to the perform by means of linkelements that are easily severed, thereby enabling the matrix to be tornaway after casing has been performed, leaving the casing inside the tubeor pipework.

Other characteristics and advantages of the invention appear from thedescription and the accompanying drawings which show preferredembodiments as non-limiting examples.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIGS. 1, 2, and 3 are diagrams showing a preform or a matrix providedwith a tubular structure of the invention, the preform or matrix beingshown respectively in its radially contracted state, in an intermediatestate, and in a radially expanded state;

FIGS. 1A, 2A, and 3A are detailed views showing how the flexible strandsconstituting the structure are braided, while in deformation statescorresponding respectively to FIGS. 1, 2, and 3;

FIG. 4 is a cutaway perspective view of a preform of the inventionpossessing a plurality of structures engaged within one another;

FIG. 5 is a cross-section on a larger scale of the preform of FIG. 4;

FIGS. 6A and 6B are diagrams showing the section of the preform whenaxially folded up in two different possible configurations;

FIGS. 7 and 7' are similar views of one or the other of the preforms ofFIGS. 6A or 6B respectively after deployment and after radial expansion;

FIG. 8 is a view similar to FIG. 2A showing a variant method of braidingthe structure;

FIG. 9 is a diagrammatic longitudinal section through a matrix and apreform, both in accordance with the invention, while the preform isbeing installed in a well, the matrix and the preform being deployed butnot radially expanded;

FIG. 9A is a detail on a larger scale of the zone of the wall of thematrix and of the preform that is referenced A in FIG. 9;

FIGS. 10, 10A, 10B, 10C, and 10D are diagrammatic views for showing thevarious successive steps in installing casing in an oil well via itsproduction tubing, and using a matrix and preform assembly as shown inFIG. 9;

FIG. 11 shows one possible way of extracting the matrix; and

FIGS. 12 and 12A show progressive inflation of a matrix during theexpansion of a preform in a well.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preform or matrix referenced 1 in FIGS. 1 to 3 is tubular in shapeand it has a braided structure. The braid is made up of two series ofinterwoven flat strands or tapes 10a, 10b which wind helically toconstitute the envelope of the structure. The two series are of oppositepitch, with the strands being inclined at an acute angle u relative to agenerator line of the resulting tube, which tube is cylindrical. Tosimplify the description, FIGS. 1 to 3 use the axis XX' of the tube as areference. The two series of strands 10a and 10b are interwoven like thecaning of a cane chair, symmetrically about the axis XX' and on eitherside thereof.

Advantageously, the angle u is about 20° (FIGS. 1 and 1A).

Each of the strands 10 is made up of a plurality of fibers or threadsthat are very strong, and that are placed side by side. They may beglass or carbon fibers having a diameter of a few micrometers, or theymay be steel wires.

As an indication, the strands 10 are 1 mm to 6 mm wide for a thicknesslying in the range 0.1 mm to 0.5 mm.

The material from which the fibers or threads forming the strands aremade preferably has a low coefficient of friction, thereby facilitatingmutual sliding between the interwoven strands, and consequentlyfacilitating deformation of the structure.

As can be seen in FIG. 2A, the braiding of the two series of strands 10aand 10b is performed with a certain amount of play, so as to give aloose assembly that leaves gaps 11 in the form of lozenges at theintersections between the two series 10a and 10b.

FIG. 1 shows a preform or a matrix in the configuration it occupies whenits length is at a maximum, L1. In this state, the structure isself-locking, the various strands bearing against one another via theirsides. The preform thus has a minimum diameter D1.

It is possible to deform this structure, e.g. by applying internalpressure thereto, as described below.

This phenomenon is shown in FIG. 2. The angle between the strands andthe axial direction XX' can be increased, with this deformation causingthe above-mentioned gaps 11 to show up. In FIGS. 2 and 2A the two seriesof strands 10a and 10b are in an intermediate position with the angle vbeing about 30° to 35°, for example. This deformation corresponds toaxial compression A of the structure and corresponding radial expansionR thereof. The structure thus has a length L2 that is shorter than L1and a diameter D2 that is greater than D1.

This deformation may continue to the state shown in FIGS. 3 and 3A wherethe structure is again locked, with the strands making up the braidagain bearing against one another as shown in FIG. 3A. The braiding ispreferably designed so that this locking effect takes place when theangle w between the strands and the axial direction lies in the range50° to 70°. The structure then has a minimum length L3 and a maximumdiameter D3.

This deformation is naturally reversible, and by pulling axially on theends of the structure shown in FIG. 3, it is possible to cause it toreturn to the state shown in FIG. 1.

The braiding shown in FIGS. 1A to 3A is simple braiding, in which astrand 10a passes in alternation over and under a strand 10b, and viceversa. Naturally, other forms of braiding could be envisaged, e.g. thebraiding shown in FIG. 8. In FIG. 8, each strand 10a passes insuccession over and under pairs of strands 10b, and vice versa.

It is appropriate to recall that the structure shown in FIGS. 1 to 3 ismerely diagrammatic, for the purpose of explaining the phenomenonwhereby the preform or the matrix is deformable.

FIG. 4 shows a preform 1 susceptible of industrial application. Itcomprises a plurality of deformable tubular structures of the kinddescribed above, and in particular it comprises four such structures 3a,3b, 3c, and 3d that are coaxial, of ever decreasing diameter, and thatare nested one within another. In practice, it is naturally possible toprovide a greater number of structures nested one within another, e.g.ten. They are confined between two skins, an outer skin 4 and an innerskin 5, both made of elastic material, e.g. an elastomer material. Therole of the inner skin could be played by the wall of the matrix. Thetubular structures are impregnated in a medium that is fluid butsettable, e.g. a thermosetting resin that polymerizes when hot, whichresin is contained between the two skins 4 and 5.

The ability of the skins 4 and 5 to deform is selected to be compatiblewith that of the braided structures 3, the assembly deforming as awhole, and with the same amplitude throughout.

Because the medium 30 is fluid, and because the structures 3a to 3d areflexible, and capable of sliding freely relative to one another, it ispossible to fold up the preform longitudinally. FIGS. 6A and 6B show twopossible ways in which it may be folded up (which ways are notlimiting), respectively into a U-shape and into a spiral (orsnail-shell) shape. After being folded in this way, it is possible togive the preform a cross-section of very small size. By being unfolded,the preform can be deployed to take up the cylindrical shape shown inFIG. 7. Thereafter, e.g. by applying pressure internally, it is possibleto cause the preform to expand radially, with each of its concentricstructures 3a, 3b, 3c, and 3d deforming in application of theabove-described phenomenon.

FIG. 9 shows a preform similar to that described above and associatedwith an expander tool designed to put it in place in a well, which toolis referred to be low as a "matrix".

As already stated, the preform 1 which is shown in its unfolded, but notyet expanded state, includes, a medium 30 of thermosetting resin whichoccupies the annular space between the two skins of elastic materialcomprising an outer skin 4 and an inner skin 5 or 71 (belonging to thesleeve 7). This gap also contains a plurality of tubular deformablestructures that are concentric and made up of braided tapes 3.

The matrix, given reference 6, comprises a tubular sleeve 7 that isclosed at its top and bottom ends by respective closure plugs 60 and 61.

The top plug 60 has a tube 8 passing therethrough with openings 80 thatopen out to the inside of the sleeve 7, as does the free end of the tube8. Appropriate means (not shown) serve to inject a liquid under pressurevia the tube 8 into the sleeve 7 via a flexible duct.

This liquid may be delivered from the surface. In a variantimplementation, use may be made of the liquid already present in thewell (mud, oil, . . . ) with said liquid being injected into the matrixby means of a pump fitted thereto.

The wall of the sleeve is constituted by two elastic membranes, e.g.made of elastomer material, an inner membrane 72 and an outer membrane71. Between the two membranes, there is disposed a tubular structure ofbraided strands of the kind described above and referenced 70. In avariant, a plurality of concentric structures may be provided that areengaged one within another, as is the case for the preform.

The length of the sleeve 7 is greater than the length of the preform 1.End plugs 60 and 61 are fixed, e.g. by adhesive, to the end zones of theinner membrane 72.

The sleeve 7 is fixed, e.g. by means of its outer membrane 71, to thepreform 1, by means of end cuffs 73 and 74. These have severing zones730 and 740, respectively. The cuffs 73 and 74 form gaskets between thepreform and the sleeve 7 constituting the matrix 6.

The interface between the outer membrane 71 of the sleeve and the innerskin 5 of the preform is treated so as to ensure that there is littleadhesion between them, e.g. by being coated in a silicone.

In an embodiment, the inner skin may be omitted.

Preferably, as can be seen in the detail of FIG. 9A, the outside face ofthe outer skin 4 of the preform has pads 40. The pads may beconstituted, for example, by annular swellings separated by grooves 41that are likewise annular. The purpose of the pads is to improve sealingwith the wall of the well, and to retain prestress and a degree offlexibility after setting.

FIG. 10 and the following figures show how an oil well can be cased viaits production tubing by means of the preform 1 and with the help of amatrix as described above.

Reference P designates the wall of the well, and reference 9 designatesthe production tubing installed in the well, the tubing being held andcentered by a hydraulic plug or "packer" 90.

As an indication, the inside diameter of the tubing 90 is 60 mm whereasthe mean diameter of the well is about 180 mm. The preform is insertedwhile folded up, e.g. in snail configuration (see FIG. 6B), so that thegreatest dimension of its cross-section is less than the inside diameterof the tubing 9. This greatest dimension may be about 55 mm, forexample. The preform is thus lowered together with the tube 9 down tothe desired level inside the well. Initially, the preform 1 is caused tobe deployed so as to take up a cylindrical shape. Its outside diameteris then 90 mm. This is achieved by injecting a fluid such as water underpressure into the sleeve 7, via the tube 8.

This fluid delivery is represented by arrows f in FIG. 10A.

Thereafter the pressure of the fluid is increased, as represented byarrows f' in FIG. 10B. This achieves radial expansion both of the sleeve7 and of the preform 1, with the braiding being deformed in the mannerdescribed with reference to FIGS. 1 to 3.

Naturally, while this radial expansion is taking place, the length ofthe preform and of the matrix decreases. The preform thus expands to adiameter of 180 mm.

The preform is thus pressed intimately against the wall P of the well.The amount of expansion that takes place depends on requirements, i.e.it is a function of the projections from the wall. This constitutes anessential difference relative to known flexible preform devices in whichradial expansion cannot take place beyond a well-defined diameter. Thepreform therefore adapts to the shape of the well as it finds it. Thisis made easier by the presence of the pads 40 which serve to provideanchoring and sealing.

Thereafter, the wall of the preform is allowed to set by injecting a hotfluid (under pressure) into the sleeve 7 and causing it to circulate.Once polymerization has terminated, the fluid contained in the sleeve issucked out, thereby causing the sleeve to shrink radially, as shown inFIG. 10C.

By applying upward traction on the tube 8, it is then possible to tearthe entire matrix away by breaking its severable connection zones 730and 740.

The sleeve 7 lengthens by shrinking radially, and it can be extractedthrough the tubing 9.

Once set, the original preform 1 constitutes part of the casing of thewell.

Such casing can be used with or without cement, depending on the groundconditions involved.

When the preform is put into place in the well, it is naturallynecessary to take account of the way in which its axial length is goingto shorten during the operation.

The method of extraction shown in FIG. 11 does not require suction to beapplied to the inside of the matrix.

Because the structure is braided, by applying traction F' to the matrix,it shrinks progressively in a radial direction, the shrinking movingdownwards, thereby separating it from the casing 1 (that has alreadyset).

Reference 7a designates the already-shrunk portion of the matrix, thathas become detached from the casing, with the strands of the structurecrossing at the angle u.

Reference 7b designates the expanded portion whose strands cross at theangle w.

FIGS. 12 and 12A show the matrix 7 and the preform 1 being expandedprogressively from the bottom upwards with an inflation liquid beinginjected via the duct 8 into the bottom portion of the matrix. Suchprogressive inflation can be obtained, for example, by enclosing thepreform and the matrix (in the folded state) in an envelope that issuitable for being torn longitudinally in an upwards direction.

Naturally, the braided deformable structure of the invention can beimplemented with preforms that are installed without making use ofinflatable matrices that themselves make use of said structure, and viceversa.

In a possible embodiment of the structure, some of the fibers in atleast some of the strands (and advantageously in all of the strands) arereplaced by electrically-conductive wires enabling the preform or thematrix to be heated for the purpose of polymerizing the preform, byconnecting the wires to an electricity supply.

This is particularly advantageous for a (reusable) matrix whereproviding electrical connections to the two ends of the structure is notparticularly difficult.

We claim:
 1. An assembly comprising a radially expandable tubularpreform for casing a well and a recoverable matrix serving as a tool forexpanding the preform, whereina) said preform possesses an inside and awall of composite material formed by a resin that is fluid and settable,said resin confined between an inner skin and an outer skin of elasticmaterial, within which there is embedded a tubular structure of flexiblestrands crossing over one another, enabling it to expand radially whileshrinking axially under the effect of pressure being applied to theinside of the preform; and b) said matrix initially secured to thepreform includes an inflatable sleeve inside the preform into which itis possible to inject a fluid under pressure in such a manner as topress the matrix radially against the inside wall of the preform causingboth the sleeve and the preform to expand radially, said matrix beingsuitable for being torn off at the end of the operation after thepreform has set.
 2. An assembly according to claim 1, wherein saidtubular structure of said preform comprises:a braid of flexible strandsmade up of fibers and includes two series of strands that cross over oneanother symmetrically relative to a longitudinal axis of the tubularstructure, the strands in each series being parallel to one another. 3.An assembly according to claim 2, wherein said preform is in itsradially contracted state, each of said series of strands forms an acuteangle lying in a range 10° to 30° and preferably about 20° relative tothe longitudinal axis.
 4. An assembly according to claim 2 or 3, whereinsaid preform is in its radially expanded state, each of said series ofstrands forms an acute angle lying in a range 50° to 70° relative to thelongitudinal axis.
 5. An assembly according to claim 2, wherein saidstrands are flat, taking a form of tapes.
 6. An assembly according toclaim 2, wherein said preform possesses a plurality of braided strandstructures engaged coaxially within one another.
 7. An assemblyaccording to claim 1, wherein said preform is sufficiently flexible tobe capable of being folded up longitudinally when it is in its radiallycontracted state.
 8. An assembly according to claim 1, wherein saidouter skin of the preform possesses patterns in relief.
 9. An assemblyaccording to claim 1, wherein said inflatable sleeve is fitted with atube for feeding fluid inside of the sleeve.
 10. An assembly accordingto claim 1, wherein said matrix is fixed to the preform by severablelink elements.
 11. An assembly according to claim 1, wherein said sleevealso possessing a tubular structure made up of flexible strands crossingover one another.
 12. An assembly according to claim 11, wherein atleast one of the strands of the sleeve is replaced by electricallyconductive wire enabling the preform to be heated for polymerizationpurposes, when said wire is connected to a source of electrical current.